Transverse magnetic traveling wave amplifiers



TRANSVERSE MAGNETIC TRAVELING WAVE AMPLlFlERS Daniel M. Lipkin,Philadelphia, Pa., assignor, by mesne assignments, to Sperry RandCorporation, a corporation of Delaware Application March 17, 1955,Serial No. 494,908

8 Claims. (Cl. 179-171) The present invention concerns a transversemagnetic traveling wave amplifier.

It is an object of the invention to provide a transverse magneticamplifier structure which will yield a substantially square wave outputpulse rather than one exhibiting exponential decay.

It is an object of the invention to provide a transverse magneticamplifier which will admit the information to be amplified as a pulsetrain in the case of ultra high frequency signals or as a signal pulsein the case of radio frequency applicable to present-day digitalcomputers, to a delay line incorporating a ferrite ferromagneticdielectric comprising, in one form a coaxial continuous parameter delayline designed around a tube of ferrite.

It is an object of the invention to provide a ferromagnetic transverseamplifier comprising a delay line in which the input informationpropagates down the delay line, and when all of the information to beamplified in one operation, comprising the propagation, is momentarilystored in a delay line, the ferrite dielectric forming a part of thedevice is suddenly exposed to an increase in the transverse magneticbias applied to it. It will be understood that the delay linedielectric, for example the ferrite mentioned above, is alwaystransversely biased magnetically in an orientation everywhere at rightangles to the direction of any magnetic field which can be produced bysignal information which propagates down the delay line. This steadyD.C. transverse bias is, at selected times, augmented by a drive currentwhich increases the transverse bias to a higher value after the mannerdiscussed in the lumped parameter forms in my copending applicationSerial No. 494,907, now Patent No. 2,811,652, for: Pulse Type TransverseMagnetic Amplifier.

The larger value of the transverse bias is maintained until all theinformation has left the delay line, after which time the transversebias can be restored to its lower steady state value to await the nextamplifying operation. The net result of this form of the invention isthat the signal information traveling down the delay line emerges at theend of the line in amplified state, that is, as the transverse bias isin the process of being increased to its high value by the drive pulse,all the current elements in the various portions of the delay line aresimultaneously magnified or amplified in exactly the same Way, and thismagnification also occurs in the case of the lumped parameter transverseamplifiers discussed in my copending application, mentioned above.

Magnetic materials having rectangular hysteresis characteristics may behere employed. For a detailed discussion of transverse magneticamplifiers in connection with the present invention, reference is madeto the following copending application:

Serial No. 494,903, for Transverse Magnetic Amplifier, filed on evendate herewith.

Like numerals in the drawings refer to like parts throughout.

Figure l is a composite loss diagram for selected magnetic materialshaving various hysteretic constants.

Figure 2 is a schematic diagram of one form of transverse traveling wavemagnetic amplifier.

States Patent Figure 3 is a modification of the showing in Figure 2 andFigure 4 is a schematic representation of a ferrite micro-second delayline according to the invention.

The basic considerations concerning transverse devices comprising thepresent invention may be formulated as follows:

(1) Transverse fields are in general applied to a core of ferromagneticmaterial simultaneously. It may be noted that the B-H relationships arequantitatively unknown except under the conditions to be describedbelow.

(2) It is possible by means of the invention to obtain quantitativelypredictable BH relationships in transverse core structures, consistingin the resultant B vector being a simple mathematical function of theresultant H vector.

(3) The above is accomplished by observing strictly the condition thatthe scalar magnitude of the vector resultant magnetizing force be keptabove a predeterminable level characteristic of the magnetic material.

A. When the above condition is met, the vector flux density B issubstantially given by the vector equation:

a B= Z where Bs is the saturation flux density magnitude for the Amaterial; H is the resultant magnetizing force vector in the material;and h is the scalar magnitude of H.

The above equation states that B is in the same direcwhere hp is thepredeterminable level referred to in 3 above.

(5) In a practical embodiment, a transverse magnetic structure,constructed in accordance with the foregoing considerations, wouldcomprise a body of magnetic material having magnetizing means associatedtherewith and adapted to impress mutually orthogonal fields on the saidbody. An output effect may be produced from such a transverse structureby varying the magnitude of at least one of the transverse fields and,so long as the condition represented by Equation 2 is satisfied, theoperation of the device will be substantially loss-less.

(6) The predeterminable level hp referred to above may be taken to bethat value of magnetizing field larger than the value at which thespecific rotational hysteresis loss for the material peaks (seeFigure 1) and for which the specific rotational hysteresis loss isappreciably less than said maximum rotational hysteresis loss.

It will be seen from the above that the mutual inductance is not theresult of a single field, but is produced by the oscillation of Bsthrough the angle 6 due to the interaction of the two fields and thechange in the resultant Hr with its effect on Bs.

The analysis of the traveling Wave transverse amplifier is complicatedby the changes in the transverse bias which also produce changes in thecharacteristic impedance and delay time of the ferrite delay line. Inthe case of traveling wave transverse amplifiers, the problem ofpreventing the feedback of energy from the output to the input or inputsource is simply the problem of how to attenuate any backward travelingwaves which may be induced in the delay line in the amplifying process.To amplify a pulse to best advantage separation between input and outputis effected by virtue, of continuity, direc tion and delay of the pulsein the line. Bias is always present and drive is applied after an inputpulse train has propagated so that it is all in the line. The drivepulse is applied and maintained until the entire pulse train has beenreceived as a signal and is out of the line. The action amplifies thesignal and time duration is decreased as seen at the output. Forexample, during the time period that the transverse bias is beingincreased, if no such backward traveling waves are generated during thisprocess, the problem reduces itself merely to that of how to terminatethe delay line correctly. One way in which backward traveling waves,originating in the amplifying process, can be attenuated is to decreasethe transverse bias to its steady state value while the backwardtraveling wave components are still in the delay line. It is, however,equally important that this action take place after the forwardtraveling waves carrying the useful output information have left thedelay line, as it is desirable that they are not also attenuated by thedecrease in bias.

This action can be accomplished by making the delay line several timeslonger than is necessary to hold the input pulse train or pulses, and topostpone the rise of the transverse bias until the pulse train nears theend of the delay line. The forward traveling waves will be amplified andimmediately emerge from the delay line while any background travelingwaves will have to travel back through the larger part of the delay lineand so will still be in the line when the transverse bias is reduced.They will then be attenuated by a process which is the reverse of thatwhich occurs when the transverse bias is increased.

In Figure 2 is shown one form of traveling wave trans verse magneticamplifier, for use with single computer pulses or radio frequencyinformation. An elongate cylindrical core 20, of ferromagnetic materialis provided with a central channel 21 threaded by a combined bias anddrive winding 22. Although. winding 22 is shown as a single turn, itmust be understood that as many turns may be employed as good designindicates. This consideration will apply throughout the other figures inthis case.

Combined bias and drive winding 22 is supplied with terminals 23, 24-for the application of appropriate voltages. Around the outer surface offerrite tube 20 is a metallic coating 25, which serves as a capacitiveground plane of the delay line. A break 26 is made in the metalliccoating to prevent or rather limit eddy currents when the longitudinalflux changes in the ferrite tube. On top of the metallic coating 25 iswound an input-output coil 27 having an input terminal 28 and an outputterminal 29. The coating 25 is grounded at 39. After the inputoutputcoil 27 has been wound, an additional conducting coating, with a gapdirectly above and corresponding to gap 26, may be applied to theoutside of the winding to increase the capacitance per unit length ofthe delay line. Such an outer coating should, of course, be grounded tothe inner coating and is indicated provisionally by the dotted line 31.

The configuration of the device shown in Figure 2 insures a relativelylong delay time for waves traveling along the helical winding 27. Wavestraveling through the bias drive winding 20, however, will travel muchmore rapidly than the signal waves travel on the helix and so willovertake those on the helix as rapidly as desired, depending upon thelength of the helical winding and because the increase in the transversebias should appear to be almost simultaneous along the entire delay linecomprising the device. A drive pulse at terminals 23, 24- occurs afteran input pulse train has propagated so that it is all in the line. Thedrive pulse augments the existing DC. bias until the entire pulse trainhas been re ceived as a signal and is out of the line.

In Figure 3, a traveling wave transverse magnetic amplifier isillustrated for use with ultra high frequency or microwave pulse trains.This type of device is applicable to radar systems and the like. Anelongate tube of ferromagnetic material id is provided with a centralchannel 41 threaded by an input-output winding 42 having an inputterminal 43 and an output terminal 44. The material of tube 40 acts as adielectric of the delay line. Tube 40 is surrounded by a conductingsheet 45 having an input 46 and an output 47 comprising the bias anddrive circuits. Conducting sheet 45 forms a single turn around theferrite tube 40 and carries the total transverse bias current, and mayalso act as the ground plane or outer conductor of the coaxial cablefrom which the structure is derived. However, it will be evident thatthis latter function could be served equally well by a conductivecoating applied to the outside of the ferrite tube and having alengthwise gap such as that shown in Figure 2, above.

In the structure of Figure 3, the signal traveling down the central wireof the coaxial line 42 is not affected by either of the following twoeffects which are present in the structure of Fig. 2. (l)Self-demagnetizing tendencies in the ferrite material at and (2)long-range inductive coupling between distant elements in the delay linethrough the agency of the ferrite tube 4t). It is true thatself-demagnetizing efiects are still present, but these affect only thebias and drive circuits of the plate 45. The use of a single wideconducting strip, such as 45, for the bias drive coil, is desirable inorder that the changes in transverse bias be applied to all elements ofthe delay line as nearly simultaneously as is possible. The bias drivesheet 45 should be made very thin in order to minimize eddy currentswhich would tend to counteract the function just mentioned. The relationof the rise time of the drive pulses applied to terminal 46 to that ofthe pulses being amplified should be as small as possible, but not sosmall as to interfere with the operation of the amplifier.

A delay line may be made of a tube coated with conductive silver painthaving a clear gap, as discussed in connection with Figure 2. Two groundleads of copper wire can be connected to or embedded in the silverpaint. The main delay helix is Wound on the coated tube and may take theform of No. 38 high frequency copper wire, close-wound in 600 turns,occupying a substantial portion of the length of the tube. An additionallayer of silver paint may then be coated on the outside of the helix,again, having an eddy current preventive gap which lies above andcorresponds to the gap of the first coating, as illustrated anddescribed in connection with Figure 2. The second coating is connectedto the first by painting over the ends of the helix, thus, effectivelygrounding both coatings by a suitable means such as 30, shown in Figure2.

Such a device is illustrated in Figure 4, in Which a ferrite core on issupplied with a coating of conducting silver paint 61 to serve as aground plane for its delay line. A clear path 62 is scratched or filedin the silver coating to break the eddy current circuit. A ground Wire63 of about 1 mil is embedded as a lead in silver coating 61. A secondground wire 64 is embedded in the opposite end of the silver coating 61.A 600-turn helix 65 is closely wound around the silver coating 61. Itwill be understood that the above values are representative and aresupplied for the purposes of illustration only. They are not to be takenas in any sense limiting.

While there have been described above what are at present believed to bepreferred forms of the invention, the disclosure will suggest variationsand equivalent structures to those skilled in the art. All such variantsand equivalent structures which fall within the true spirit of theinvention are intended to be covered by the generic terminology of theappended claims.

I claim:

1. A traveling wave transverse magnetic amplifier comprising a saturablemagnetic element, a plurality of Winding means linked to at least a partof said element for producing magnetic fields respectively in first andsecond transverse directions of magnetization in the same part of saidelement, means for energizing at least a part of each of said windingmeans simultaneously and at least a part of each of said winding meansin a varying amount to produce varying fields in both said directionsand with the energizations being such that the net netizing forceproduced by said winding means when energized is sutficient to drivesaid same part of said element to substantial saturation, a conductiveelement mounted adjacent said magnetic element in capactive relation toat least one of said winding means, and means for deriving from a partof one of said winding means output signals that vary in accordance withthe variations in energization of the other of said winding means, saidoutput signal deriving means including a common return circuit connectedto said conductive element.

2. A delay line comprising an element of magnetic material, means forapplying a first magnetic field to said element including a firstwinding means, and a first means for energizing said first windingmeans, means for applying a second magnetic field to said elementsimultaneously with said first field including a second winding means,and a second means for energizing said second winding means, said firstand second Winding means being linked to said element in transversedirections so that said fields are non-parallel and intersect each otherat an angle in said material, the energizations supplied by said firstand second energizing means being such that the field in each of saiddirections has a variable magnitude and said fields have a movingresultant that saturates said element and the resultant saturatedmagnetic flux moves and tends to follow the movement of the resultant ofsaid fields whereby operation of the amplifier is in the region ofdecreasing rotational hysteresis loss, a conductive element mountedadjacent said element in capacitive relation to one of said Windingmeans and connected in circuit therewith, and means for deriving outputsignals connected to one of said Winding means.

3. A transverse magnetic amplifier delay line comprising, incombination, a magnetic core, a bias and drive winding means linkingsaid core along a first axis, means for energizing said bias and drivewinding means to produce a saturating bias field which carries the corematerial into the region of efiective clamping action between theresultant saturating magnetizing field and the saturated magnetic fluxand into the region of vanishing hysteresis loss for energizing saidbias and drive winding with alternating current for superimposing analternating field on said bias field to produce a variation in theamplitude of the resulting magnetizing field within said region ofeffective clamping action, winding means linking said core along asecond, transverse axis, a circuit connected to said second axis windingmeans and having signal input terminals, and means connected to saidsecond axis winding means including an output terminal for deriving anoutput signal, artificial delay line means including, a conductiveelement mounted adjacent said magnetic element in capacitive relation tosaid second axis winding means and connected in a common circuit pathwith one of said input terminals and with said output means, and meansconnected to said input terminals for applying thereto input signalscausing changes in direction of the resultant saturating magnetizingfield and the saturated magnetic flux clamped together, wherebyamplified output signals are produced in accordance with said inputsignals.

4. The combination of claim 3, wherein said core is tubular and made ofa ferrite dielectric material and arranged as a dielectric for thecapacitance of said conductive element and second axis winding means,one of said winding means extends axially and the other around saidcore, and said conductive element includes a layer of conductivematerial mounted around a surface of said core.

5. The combination of claim 4, wherein said conductive layer has itsends spaced apart axially along said core to reduce eddy currentstherein.

6. The combination of claim 5, wherein said conductive layer is acoating of metal attached around the outside of said tubular core.

7. The combination of claim 6, wherein said conductive coating is acoating of silver paint with an unpainted path extending axially thelength thereof, and said common circuit path includes a ground wireembedded in said coating.

8. A transverse magnetic amplifier delay line comprising a saturablemagnetic element in the form of a tube, a plurality of winding meanslinked to at least a part of said element for producing fieldsrespectively in first and second transverse directions of magnetizationsin the same part of said element, means for energizing at least a partof each of said winding means simultaneously and at least a part of eachof said winding means in a varying amount to produce varying fields insaid directions and with the energizations being such that the netmagnetizing force produced by said winding means when energized issufficient to drive said same part of said element to substantialsaturation and to produce a resultant magnetization that varies indirection with variations in said first direction field, means forderiving from a part of one of said winding means output signals thatvary in accordance with variations in direction of said resultantmagnetization, and artificial delay line means including a conductiveelement mounted adjacent said magnetic element in capacitive relation toat least one of said winding means, said conductive element includingone of said winding means in the form of a conductive sheet around saidtubular magnetic element.

References Cited in the file of this patent UNITED STATES PATENTS1,794,717 Lindenblad Mar. 3, 1931 2,543,843 Frosch Mar. 6, 19512,619,537 Kihn Nov. 25, 1952 2,650,350 Heath Aug. 25, 1953 2,723,353Spitzer Nov. 8, 1955 2,752,559 Lipkin June 26, 1956 OTHER REFERENCESCommunications and Electronics, January 1954, pp. 822-830,Nondestructive Sensing of Magnetic Cores, by Dudley A. Buck and WernerI. Frank.

